1. Field of the Disclosure
The present disclosure generally relates to the field of computer systems of enhanced integrity and corresponding mechanisms implemented therein, which may enable the provision of enhanced security standards, thereby enhancing efficiency of applications requiring a secure computer platform.
2. Description of the Related Art
The widespread use of computer systems has led to a significant increase of information processing on the basis of electronic computer systems, thereby involving the creation, distribution and processing of very large amounts of digital data. With the increasing resources of computer systems in view of data storage capacity and increased processing speed, the reproduction of large data sets, such as audio data, movies and the like, has become available for an increasing number of persons and is frequently practiced despite any protective rights, which may be associated with many of the data provided in electronic form. Thus, significant economic damage may be created by the illegal copying, storage and redistribution of electronic data. Furthermore, the distribution of application programs over widespread networks, such as the internet, may also provide the possibility of distributing malicious software applications, which may in turn be used for manipulating data and/or the configuration of a respective computer platform. For example, significant damage may be created in private environments, and in particular in the industry, by introducing software applications which may, for instance, manipulate software files such as stored data, communicate information via the internet without knowledge of the actual user of the platform, start a denial of service attack, thereby possibly rendering the platform to be no longer usable for a dedicated application requiring a specific status of the platform.
For these reasons, great efforts are being made in developing mechanisms for enhancing integrity of the computer platforms to reduce the probability for “successful” external attacks, for instance in the form of malicious software, denial of service attacks, sniffing, spoofing and the like, and also to enhance data integrity with respect to internal manipulations of the computer platform. For example, a plurality of encryption techniques are available, such as symmetric or asymmetric encryption/decryption techniques which enable the exchange of data with a high degree of resistance against tampering data by a third party during the transmission and storage of data. For example, in asymmetric encryption techniques, a pair of a private key and a public key may be used for encrypting data by means of one of the keys and deciphering the data by using the other key, wherein one of the keys may be publicly accessible. Although these techniques may provide enhanced integrity in data communication and data storage, the actual configuration of a computer platform under consideration may still provide the possibility of a plurality of attacks, in particular, as many applications intended for increasing computer security may rely on a trusted platform configuration.
A trusted computer platform may be considered as a computer system in which the hardware configuration as well as the software applications may be assumed to be in a dedicated configuration. However, a secure platform configuration may be established only by establishing a “chain” of trusted platform levels, wherein each subsequent level may be initialized by the preceding level only, if the integrity of the subsequent level has been verified. Hence, the integrity at system level may be preserved through a chain of integrity verifications wherein a root of the chain of verification steps may have to be provided with a high degree of tamper resistance so as to also accomplish a high confidence with respect to integrity of the system after initializing the highest level, i.e., the level of user applications.
In a typical computer platform, the initialization of the system requires various degrees of abstraction, for example with respect to initializing the central processing unit (CPU), initializing the system memory, which is typically provided externally to the CPU, loading an operating system into the system memory from an external mass storage device, and finally executing user applications. Thus, in view of enhancing the overall integrity of the system as a whole, it may not be sufficient to assume that the various system activities prior to loading the operating system can be considered to be secure so as to rely on the integrity of the operating system and the user application, since the operating system may be invoked by a “mistrusted” process, thereby providing the opportunity of manipulating the basic platform configuration by modifying hardware and software components. Hence, the process of initializing the various hardware components of the computer system, such as the system memory and the execution of the instructions contained therein for initializing the higher system levels, which may also be referred to as boot strapping or booting, may have to be incorporated into the chain of trust to provide enhanced overall system integrity.
A typical start sequence for initializing a computer system after applying power or after a reset event causes a “power on self-test” of the CPU, wherein also the processor starts execution of instructions at a dedicated entry address that is indicated by the processor's reset vector. That is, after an initial processor self-test, the execution of instructions may start at the entry point which may typically be an address of a software routine, frequently referred to as BIOS (basic input/output system), which may be stored in a dedicated external non-volatile memory of the computer platform. Under the control of the BIOS, the remaining self-test may be performed and the hardware configuration of the platform may be determined or “measured.” Thereafter, a search for a bootable device may be performed, such as a mass storage device, for instance the hard disk of the computer system, a disk, a CD-ROM, an extension card and the like, from which a primary boot block may be loaded into the system memory, wherein control is then passed to the primary boot block, which may load an operating system into the system memory.
Although great efforts have been made in also enhancing security of the entire boot process, it is difficult to provide a reliable core root of trust for measurement (CRTM) for the boot process, for example in view of platform modifications such as replacement of the non-volatile memory chip including the BIOS software, since a corresponding chip replacement may therefore interrupt the chain of trust, thereby also rendering all subsequent verification steps as not trustworthy.
The present disclosure is directed to various devices and methods that may avoid, or at least reduce, the effects of one or more of the problems identified above.